This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The chemical synthesis of proteins allows us to understand the chemical basis of protein function in unique ways. Ongoing projects are the following: i. Application of racemic protein crystallography to determine the X-ray structure of protein molecules, which are otherwise difficult to crystallize. Crystallization of a protein molecule from a racemic mixture {i.e. a solution containing equal proportions of L- and D- protein enantiomers} can greatly facilitate the formation of highly ordered centrosymmetric crystals. The availability of centrosymmetric protein crystals can in turn facilitate ab initio structure solution by direct methods. We have recently demonstrated this racemic approach by producing centrosymmeric protein crystals of Snowflee antifreeze protein, antimicrobial microprotein plectasin, omwaprin and several difficult to crystallize ion channel ligands from our laboratory. To explore the general utility of this racemic method we are currently applying this to other chemically synthesized proteins, which are known to be recalcitrant to crystallization in their wild type form alone. The list of protein targets currently being explored in our laboratory includes the largest ever known natural cyclotide palicourein, proinsulin, glycoprotein I-309 and a hypothetical protein from mycobacterium tuberculosis Rv1738. We are also extending this method to obtain crystals from a quasi-racemic mixture of D-protein and an analogue of L-protein. ii. Elucidation of molecular details of HIV-1 protease catalysis, an important target in AIDS chemotherapy. Various chemical analogues have been synthesized to perform 'dynamics/function'correlations in catalytic mechanism as well as totally artificial tunable catalytic apparatus have been designed and incorporated. We are currently using X-ray crystallography to elucidate the molecular details of HIV-1 protease catalysis.